Allocation and plots improvements. Version 3.6.2

[laresbernardo]

• fix: issues on several robyn_allocator() specific cases (Budget Allocator issue #349 Budget Allocation: budget constraint not hold #344 The presence of some zero coefficients might cause robyn_allocator to report all coefficients are zero #345), especially when some coefficients were 0
• feat: new date_min and date_max parameters on robyn_allocator() to pick specific date range to consider mean spend values (user request). Also, a new plot method for robyn_allocator() outputs.
• viz: removed redundant information, improved and standardized all plots styles and contents
• feat: provide recommendations on calibration inputs depending on the experiments' confidence, spending, and KPI measured (Robyn_refresh error when collection results #307)
• fix: bug with Weibull adstock scenario (Demo example with weibull adstock failes with error: "'from' must be a finite number" #353)
• feat: warn and avoid weekly trend input when data granularity is larger than "week"